1. Field of the Invention
The present invention relates to an image processing apparatus for determining the type of an original and an image processing method.
2. Description of the Related Art
A scanner is used widely, which reads a target original by irradiating the original with light from a light source, reading a reflected signal value, and forming an image. As an original a user causes a scanner to read, mention is made of various originals, such as paper on which a photo is printed, printed matter, such as a magazine and a map, and a general written original. Because of this, it becomes necessary to determine the type of an original.
For example, the problem of color reproducibility at the time of scanning various kinds of originals is widely known. The spectral sensitivity of observation by human eyes and the spectral sensitivity of a scanner reading an original do not agree with each other. Because of this, color reproduction is performed by performing color conversion processing so as to match the sensitivity of a scanner scanning an original image with the sensitivity of human eyes. However, in the case where color conversion processing is performed on originals of the same type having the same spectral characteristics, there arises no problem, but in the case where the same color conversion processing is performed on various kinds of originals having different spectral characteristics, a deviation occurs in color reproducibility.
In particular, the spectral characteristics of an original of a printing sheet, such as plain paper are quite different from those of an original of a photographic sheet, such as glossy paper, and therefore, in the case where the same conversion table is applied in color conversion processing, a large deviation occurs in color reproducibility. For example, despite having created a color conversion table that is adjusted to an original of a printing sheet, in the case where the color conversion table is applied to an original of a photographic sheet, the result of color reproduction will be that a color difference ΔE is 7 or more on average. Because of this, it is necessary to accurately discriminate between an original of a photographic sheet and an original of a printing sheet and to perform color conversion processing in accordance with the type of the original in order to prevent a deviation in color reproducibility from occurring.
As an original-type determining method, there is a method in which the surface condition of a paper surface is read and a determination is performed based on the surface roughness and the surface shape (see Japanese Patent Laid-Open No. 2004-042370). Specifically, by taking the depth of the surface irregularities to be a feature of the surface roughness and the period of the surface irregularities to be a feature of the surface shape, the type of an original is determined by paying attention to these features. In general, plain paper has the features that the surface irregularities are deep and the period of irregularities is short. For these features, detection of the period of irregularities by utilizing a run-length and the number of times of change, Ra measurement, and estimation of the depth of irregularities by a histogram are performed.
However, Japanese Patent Laid-Open No. 2004-042370 has not taken into consideration the directional properties of fiber, etc. Further, there is a case where, for example, an original is placed in various directions with respect to an original table. Because of this, in a read image, the direction of fiber of the paper can take various directions as a result and in this case, the period of the irregularities of the paper surface may also be different depending on the direction of fiber. However, Japanese Patent Laid-Open No. 2004-042370 has not taken into consideration the directional properties of fiber as described above, and therefore, there is a case where an erroneous determination of an original is caused because the run-length or the number of times of change beyond expectation is detected. In particular, an erroneous determination due to the influence of the directional properties of fiber is easily caused between coated paper and glossy paper whose features, such as the surface roughness and surface shape, are close to each other.